Two isoforms of a heme oxygenase gene,ho1andho2, with 51% identity in amino acid sequence have been identified in the cyanobacterium Synechocystissp. PCC 6803. Isoform-1, Syn HO-1, has been characterized, while isoform-2, Syn HO-2, has not. In this study, a full-lengthho2gene was cloned using synthetic DNA and Syn HO-2 was demonstrated to be highly expressed inEscherichia colias a soluble, catalytically active protein. Like Syn HO-1, the purified Syn HO-2 bound hemin stoichiometrically to form a heme–enzyme complex and degraded heme to biliverdin IXa,CO and iron in the presence of reducing systems such as NADPH⁄ferredoxin reductase⁄ferredoxin and sodium ascorbate. .
